Based On The Reliability Theory The Safety Assessment And Analysis Method Of The Loess Tunnel Lining’s Structure

As the special soil tunnel, loess tunnel was greatly different with other tunnel and thesoft soil unnel in south,due to the physical-mechanical properties and stronger watersensitivity peculiar to the loess, a lot of difficulties were given to the loess tunnel in term oftunnel lining structure reliability analysis and application. Therefore, based on the engineeringstructure reliability theory knowledge, the paper carried out research about the loess tunnelstructure reliability and other related issues,it does specific research work in following severalmain aspects:1.The mechanical characteristics and damage mechanism of the loess tunnel liningstructure under the constant value design parametersIn order to research the mechanical characteristics and damage mechanism of the loesstunnel lining structure, this paper independently develpoed the programme that was applicableto simulation analysis and calculation for effect of an actionof loess tunnel lining structure,and it was based on load-structure model, the program mainly considered the constantcondition about the design parameters and the physical mechanical parameters of surroundingrock,when the tunnel lining structure was designed. Then this paper used the program tosimulate and calculate typical section loess highway tunnel lining structure, according to theloess inherent engineering characteristics,and summarized the forces and damagecharacteristics of loess tunnel lining structure under the constant design parameters, andcombined with the safety factor of the calculation from the program, finally,it summarizedloess tunnel the most unfavorable position under load,for future these necessary designingexperience was given to designers in designing the loess tunnel support parameters.At thesame time, it had an important guiding significance for the safe construction of the loesstunnel lining structure.2. Practice and study about the structure reliability theory applying to the loess tunnelstructure design(1) Due to complexity and variabilityof the loess’s physical and mechanical parameters,and lesser test data of the loess strata parameters, therefore, through consulting the existingtest informations and some research results, the paper used mathematical statistics knowledgeto do analysis,and got the probability distribution of the types and their mathematicalcharacteristic value about the loess strata parameters, these research achievements offered thenecessary data base for the loess tunnel structure reliability subsequent analysis, and theparameters also were got by this paper for the first time.At the same time, these statisticalcharacteristic value and probability distribution offered convenience for studying thereliability of other building structures in loess area.(2) In allusion to probability and statistics analysis of the loess tunnel’s surrounding rockpressure, the paper took examples from the method of calculating the deep tunnel’ssurrounding rock pressure in probability limit state method offered by the relevant designspecifications,and considered the primary and secondary relations between the variability of the loess tunnel collapse and that of the surrounding rock density.finally,the paper obtainedthe statistical characteristic values of the surrounding rock pressure and the probabilitydistribution types, that would solve the problems of load and probability distribution types.Then, based on Monte Carlo finite element method and combined with Load-StructureModel,this paper developed six main programs,such as the numerical simulation finiteelement program about the tunnel lining structure’s effect of actions and the generationprogram about random variables,by these programmes this paper realized calculation andanalysis about the reliability of the loess tunnel lining structure, and it provided a simple andpractical calculation method for analysing reliability of other tunnel lining structure for future.(3) Through the application of the above programmes, the reliability index of all crosssection of typical section loess highway tunnel lining structure could be got, the papercompared them and experience indexs, in order to evaluate whether designing the tunnellining structure is reasonable and safe. At the same time,the paper compared the conclusionsthrough traditional security coefficient method and the deducing throug the reliability indexescarefully,in order to improve that the method of structure reliability theory was feasible in thetunnel structure design stage, and also was accurate. a new method of structure reliabilityanalysis and evaluation was offered to design phase of the tunnel structure.3.Analysis and applied research on the commissioned loess tunnel structure reliabilityContraposing evaluation the reliability of commissioned QinDong loess tunnel liningstructure, this paper put forward beginning from the lining’s thickness, got tunnel thicknessactual size by the geological radar, and through comparing the design size of the tunnel withactual size with the reliability theory,then the paper analsed and calculated them, and then thepaper evaluated the safety and reliability of the tunnel lining structure in operation phase, thiswas a simple and feasible method proposed by the paper of evaluating reliability of thecommissioned loess tunnel structure, this method provided a feasible method for evaluatingreliability of other tunnel lining structure the subsequent for future. At the same time, thisarticle from the structure reliability probability, thouhgt this structure is safe and reliable whenthe structure reliability probability is95%, therefore, the minimum thickness of the liningcould be is inferred from the known reliability indexes of tunnel lining structure,and then thatit was carried as the tunnel lining’s thickness during tunnel construction was absolutelyeconomic security,this is fully verified bu the paper.Thus, this paper put forward that if thetunnel was constructed according to the minimum thickness of the lining proposed by theknowledge of the strucutre reliability probability, the necessary security of the structure couldbe ensured,and the construction cost could be reduced effectively. In term of reducingconstruction cost during constructing tunnel for future, this also has the guiding significance.